The present invention relates to an improvement in a shut off apparatus for a fluid passage and a method of opening and closing the apparatus. The present invention particularly relates to a shut off apparatus in which a fluid passage is opened or closed by thawing or freezing fluid flowing through the fluid passage.
Shut off apparatus for various separating and analyzing instruments which deal with organism specimens, such as cells and proteins, are required to have the following functions: firstly, the apparatus has little irregularity in passage walls thereof, and organism specimens adhered to the passage walls can be cleaned with ease; secondly, little damage is provided to an organism specimen used in opening or closing the apparatus; and lastly, it is possible to simultaneously open or close a plurality of passages since those instruments can perform such an operation.
A typical example of such an apparatus is disclosed in Japanese Patent Unexamined Publication No. 60-199564, for example, in which a passage is closed or opened by freezing or melting the fluid flowing therethrough.
This apparatus, however, has a problem in which it is not possible to confirm that the fluid in the apparatus has actually frozen and the passage is closed upon cooling the apparatus to close the passage. This problem results for the following reason. When the fluid is rapidly cooled it does not effect the closing function of the passage at a freezing point thereof in a transient stage and it primarily effects the closing function only when the adhering force of the frozen portion of the fluid to a passage wall becomes larger than the force due to the flow of the fluid.
For this reason, the fluid must be rapidly cooled below the freezing point thereof to close the passage and the cooling means should be always supplied with electric power also after the passage is closed. Therefore, the temperature of the apparatus or that of the fluid further drops after the passage is closed, and the fluid is cooled to a low temperature considerably below the freezing point of the fluid.
The cooling means is thus provided with electric power more than that necessary for the freezing of the fluid in order to maintain the closing function of the fluid after the passage is closed. Moreover, because it is necessary to raise the temperature of the apparatus, which has been cooled too low, to above the freezing point in opening the passage by thawing the fluid by heating, it takes a lot of time to thaw the fluid, so that the apparatus is deteriorated in its ability to respond quickly and efficiently in thawing of the fluid.
Accordingly, it is an object of the present invention to provide a shut off apparatus for a fluid passage and method of controlling the apparatus which enables low consumption of electric power for maintaining the closing state thereof after the passage is closed.
Another object of the present invention is to provide a shut off apparatus for a fluid passage and method of controlling the apparatus which is enhanced in responsiveness in thawing of the fluid.
Still another object of the present invention is to provide a method of confirming the closing of the shut off apparatus.